Heat treatment of magnesium base alloys



March 23, 1943.

A. BRANDT HEAT TRIilAEIIMEll'l QF MAGNESIUM BASE ALLOYS Filed Oct. 8,1941 BCDEFGH 3mm: W364 m&z

Patented Mar. 23, 1943 HEAT TREATMENT OF MAGNESIUM BASE ALLOYS AlfredBrandt, Swansea, Wales, assignor, by mesne assignments, to The AngloCalifornia National Bank of San Francisco, San Francisco, Calif., anational banking association, as trustee Application october 8, 1941,Serial No. 414,176 In Great Britain September 9, 1940 2 Claims.

This invention relates to high percentage magnesium base alloys and isparticularly concerned with raising the yield point (proof stress) ofthe alloys by subjecting the same in the as-cast" condition to asingle-step heat treatment within a range of not less than 100 C. butless than 250 C., having avoided any previous thermal treatment athigher temperatures.

It is an object of the present invention to avoid the so-called solutionheat treatment at temperatures far above 250, which constitutes, withsubsequent chilling, the first stage of the thermal treatment ofmagnesium bas alloys which has therefore been the standard practice intreating castings of this type, an annealing treatment at a lowertemperature,' below 200 C., being preferably carried out as a secondstage. The singlestep thermal treatment at low temperatures leaves thestrength of the material substantially unaltered, and the elongation mayeven decrease to some extent. On the other hand, the yield point ismaterially increased. Uniformity of results, reduction of wastage, thelessening of fire risks, are also possible-advantages.

According to the present invention, the singlestep heat treatmentbetween 100 C. and 250 C. is applied to magnesium base alloys containingmore than 7% but less than 12% of aluminum,

' plus at least about 0.2% and less than 4% zinc,

and also containing from 0.1% to 1.0% of manganese. the total amount ofalloying constituents being not'above 12%.

The following examples illustrate various indinates corresponding toyield point in tons per square inch.

Turning now to the figure of the drawing and reading from the left, theefiect of the heat treatment of magnesium base alloy castings A to Hinclusive of the hereinafter appearing table is illustrated. Th top lineof each of the various columns in the drawing indicates the yield point(tons per square inch, for 0.1% permanent deformation) of theheat-treated casting, the line in the same column somewhat below itindicating the yield point of the unheat-treated alloy, that is to say,the alloy in the condition resulting from casting, or in other words,the condition known as as cast" condition.

The table given below contains the percentages by weight of "thecastings subject totolerance for usual impurities together with the heattreatment which they received, namelyz' Heat treatment in days at 0.

3x140 3x140 2x140 3x140 3x175 1x240 1x240 3x175 In preparing the aboveexamples and diagrams, alloys were made up and cast into tensile testbars in accordance with the specifications of the British Air MinistryDepartment of Technical Development. 0.1% yield point was determined inthe case of each alloy in the "as cast con-, dition, and after heattreatment at C. for 1, 2 and 3 days, after heat treatment at C. for 1, 2and 3 days and after heat treatment at 240 C. for 1, 2 and 3 days.Duplicate tests were carried out in each case.

I claim:

1. A method for improving the yield point of cast magnesium base alloyscontaining more than 7% but less than 12% of aluminum, at least about0.2% and less than 4% of zinc and from 0.1% to 1.0%.of manganese, thetotal amount of alloying constituents being not above 12% the balancebeing substantially all magnesium, which comprises subjecting suchalloys in the as-cast condition to a heat treatment at a temperaturewithin the range of 100 C. to 250 C.

2. An alloy consisting principally of magnesium and containing from '7to 12% of aluminum, at least about 0.2% and less than 4% ofzinc and from0.1% to 1.0% of manganese,- and the balanc substantially all magnesium,the total amount of alloying constituents not exceeding 12%, in the formof shaped castings the yield point of which has been raised withoutappreciable increase in strength by heat treatment in the as-castcondition at a temperature within the range of 100 C. to 250 C.

ALFRED BRANDT.

